This invention is concerned with a prosthetic replacement device and more particularly a total knee joint, providing simulation of the normal movement characteristics of the articulating surfaces of the natural knee joint, in particular rotation and derotation during flexion and extension. While the knee joint is usually considered to be a hinge joint, which implies that its movements are flexion and extension about a horizontal axis, the large size and incongruent shapes of the articulating condylar surfaces of the femur are such that the normal movement of the knee also allows for controlled rotation and the translatory movement of the knee joint actually occurs about three spatial axes.
A large number of various forms of knee arthroplasty have been proposed in recent years in an attempt to provide the equivalent of these general patterns of movement and articular geometry. Generally, there are two major types of knee prostheses: hinged and non-hinged. In one form, the knee is resected and replaced by a metal hinged-type device with deep penetration of the intermedullary canal in both the femur and the tibia by means of flared and thick distal fixation stems. Such devices have been previously decribed by Shiers, Young, and Walldius. While these devices provide stability during flexion-extension of the knee, they only permit motion about a single axis and do not allow for abduction-adduction rotation during flexion and extension. The range of movement is limited and patients are seldom able to flex the knee beyond 90.degree.. Moreover, implantation requires the removal of a significant amount of the bone with a shortening of the limb if for any reason the prosthesis must be removed for subsequent arthrodesis.
More recent prostheses using a different approach attempt to structurally resurface both of the articulating surfaces of the knee to provide a non-hinged type prosthesis. Such devices have been previously described as unicondylar, such as the POLYCENTRIC prosthesis, or dual condylar, such as the GEOMEDIC prosthesis. Each, however, relies upon identical femoral condylar articulating surfaces with identical longitudinal and transverse cross-sections. Such condylar articulating features are different from the normal knee and they do not allow for the same movement found in the normal knee, providing only a partial duplication of the natural knee movement.
Still others create a mold of the distal femoral condyles providing circumduction in different planes and requiring the use of a long intermedullary canal stem and severance of both the collateral and cruciate ligaments. Such devices have been described by Ewald, Helfet, Aufranc and Turner. Even with the use of methylmethacrylate for cement fixation, these devices have unstable characteristics since the complexity of the knee movement tends to cause considerable torsional stress and eventual wear and weakening of the joint.